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The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s−1. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s−1 communication., QC 20240927

We summarize our recent experimental studies of free-space communications enabled by directly modulated quantum cascade lasers at both MWIR and LWIR regions. Different detector types with different characteristics are compared., QC 20240612

This study explores the potential of long-wave infrared free-space optical (FSO) transmission that leverages multilevel signals to attain high spectral efficiency. The FSO transmission system consists of a directly modulated-quantum cascade laser (DM-QCL) operating at 9.15 mu m and a mercury cadmium telluride (MCT) detector. To fully understand the system, we conduct measurements on the DM-QCL chip and MCT detector and assess the overall amplitude response of the DM-QCL, MCT detector, and all electrical components. We apply various signals, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), 6-level PAM (PAM6), and 8-level PAM (PAM8) to maximize the bit rate and spectral efficiency of the FSO transmission. Through a two-dimensional sweeping of the laser bias current and MCT detector photovoltage, we optimize the transmission performance. At the optimal operation point, the FSO system achieved impressive results which are up to 6 Gbaud OOK, 3.5 Gbaud PAM4, 3 Gbaud PAM6, and 2.7 Gbaud PAM8 signal transmissions, with a bit error rate performance below 6.25% overhead hard decision-forward error correction limit when the DM-QCL operates at 10 degrees C. We also evaluate the eye diagrams and stability of the system to showcase its remarkable transmission performance. Our findings suggest that the DM-QCL and MCT detector-based FSO transceivers offer a highly competitive solution for the next generation of optical wireless communication systems., QC 20231115

Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching., QC 20231013

We experimentally demonstrate a Long-Wave IR FSO link with a 9.15-hm directly modulated quantum cascade laser at room temperature. Up to 8.1 Gb/s PAM8 transmission over 1.4 meter is achieved with a wideband MCT detector., QC 20230810

GaAsP/Si with high crystalline quality fabricated by cost-effective heteroepitaxial technology is a promising pathway for realizing low-cost Si-based tandem solar cell with efficiency higher than 30%. Herein, hydride vapor-phase epitaxy is used to perform selective area growth of GaAsP with high lateral coverage, referred to as epitaxial lateral overgrowth (ELOG). The ELOG is performed on GaAs-based substrates as a prestudy, followed by GaAs/Si and GaAsP/Si seed wafers employing chemical mechanical polishing to fabricate full 2 00 GaAsP/Si templates. These are subsequently used to grow and process GaAsP/Si pn-junction structures for electrical characterization. The ELOG GaAsP is studied by spatially resolved photoluminescence (PL) mapping and high-resolution X-ray diffraction measurements. PL analysis of the GaAsP/GaAs ELOG samples reveals an enhanced P-incorporation during lateral growth of GaAsP. This is also observed for the GaAsP/Si ELOG templates along with evidence of improved material quality, clearly distinguishing the laterally grown GaAsP from the planar growth directly above the Si substrate. Leakage pathways causing reduced electrical performance of the ELOG GaAsP/Si pn-junction structures are identified., QC 20230607

High bitrate mid-infrared links using simple (NRZ) and multi-level (PAM-4) data coding schemes have been realized in the 8 pm to 14 pm atmospheric transparency window. The free space optics system is composed of unipolar quantum optoelectronic devices, namely a continuous wave quantum cascade laser, an external Stark-effect modulator and a quantum cascade detector, all operating at room-temperature. Pre- and post-processing are implemented to get enhanced bitrates, especially for PAM-4 where inter-symbol interference and noise are particularly detrimental to symbol demodulation. By exploiting these equalization procedures, our system, with a full frequency cutoff of 2 GHz, has reached transmission bitrates of 12 Gbit/s NRZ and 11 Gbit/s PAM-4 fulfilling the 6.25 % overhead hard-decision forward error correction threshold, limited only by the low signal-to-noise ratio of our detector., QC 20230626

Orientation-patterned gallium phosphide (OP-GaP) has been grown heteroepitaxially on OP gallium arsenide (GaAs) templates using hydride vapor phase epitaxy (HVPE). The effect of OP-GaAs template fabrication methods of epitaxial-inversion and wafer bonding on the heteroepitaxial OP-GaP growth has been investigated. OP-GaP layers with a growth rate of up to 35 mu m/h and excellent domain fidelity were obtained. The growth rate and the domain fidelity have been revealed/studied by scanning electron microscope (SEM). In addition, we demonstrate that the crystalline quality of the individual domains, namely, the substrate-oriented domains (ODs) and the inverted domains (IDs), can be investigated by high-resolution x-ray diffraction reciprocal space mapping (HRXRDRSM), which can also indicate the domain fidelity. Attempts to increase the growth rate and improve the domain fidelity by increasing the III and V group precursors resulted in either an increase in the growth rate in the OP-GaP layers grown on epitaxial inversion OP-GaAs template at the expense of the domain crystalline quality and fidelity or an improvement in the crystalline quality of the domains at the expense of the growth rate in the OP-GaP layers grown on wafer-bonded OP-GaAs templates. In the case of OP-GaP grown on OP-GaAs templates prepared by epitaxial inversion, the crystalline quality of the ODs is better than that of the IDs, but it shows that the quality of the inverted layer in the template influences the quality and fidelity of the grown domains. To the authors' knowledge, exploitation of HRXRDRSM studies on OP-GaP to establish the crystalline quality of its individual domains (ODs and IDs) is the first of its kind. OP-ZnSe grown on OP-GaAs templates has also been included in this study to further emphasize the potential of this method. We propose from this study that once the growth rate is optimized from SEM studies, HRXRDRSM analysis alone can be used to assess the structural quality and to i, QC 20230316

High crystal quality GaAsP/Si fabricated by cost effective heteroepitaxial technology is promising to realize low-cost Si based tandem solar cell with efficiency higher than 30%. In this work, epitaxial lateral overgrowth (ELOG) of GaAsP/GaAs and GaAsP/GaAs/Si by hydride vapor phase epitaxy (HVPE) and their properties are studied by photoluminescence (PL) mapping. High crystal quality ELOG GaAsP/Si is obtained with enhanced PL intensity and narrow line width indicating reduced defect density provided by ELOG approach., QC 20230622

In this report, we summarize our recent achievements in free-space communications in the mid-infrared (MIR) region enabled by directly modulated quantum cascaded laser (QCL) at 4.65 mu m (similar to 65 THz). We have experimentally demonstrated a multigigabit free- space transmission link in the lab environment with the QCL operating at room temperature. The QCL chip is mounted on a commercial QCL mount with a water-cooled Peltier element. Multilevel modulation formats at different baud rates are generated and combined with the laser driving current at a custom-made bias-tee to drive and modulate the QCL. A commercial mercury cadmium telluride (MCT, HgCdTe) photovoltaic (PV) MIR detector with a built-in trans-impedance amplifier was used to receive the MIR free-space signal. With the receiver to be the bottleneck of the system bandwidth, the end-to-end 3-dB bandwidth was measured to be around 320 MHz, and the 6-dB bandwidth was around 450 MHz. We have successfully demonstrated up to 6 Gbps free space transmission with multilevel modulation formats, assisted with effective digital equalization techniques despite the limited bandwidth., QC 20220406

Direct heteroepitaxy and selective area growth (SAG) of GaP and GaAs on Si(100) and Si(111) are implemented by low-pressure hydride vapor phase epitaxy (LP-HVPE), which are facilitated by buffer layers grown at 410–490 °C with reactive gas mixing directly above Si substrates. High-density islands observed on GaP buffer layers on Si result in rough morphology and defect formation in the subsequent GaP layers grown at 715 °C. The impact of growth temperature of GaAs buffer layers on the crystal quality of GaAs/Si is studied. A decreased nucleation temperature significantly improves the morphology and crystalline quality of the overall GaAs growth on Si. It is observed that Si(111) substrates are favorable for both GaP and GaAs growths in comparison with Si(100). In SAGs of GaP/Si and GaAs/Si, the high selectivity innate to HVPE is maintained in the used unconventional growth regime. The spatially resolved photoluminescence mapping reveals the material quality of GaAs/Si is enhanced by defect filtering by SAG. The outcomes of this work will pave the way of III–V/Si integration realized by cost-effective HVPE for photonic device applications., QC 20210323

We report on an experimental demonstration of a mid-infrared free-space communication link enabled by a directly modulated quantum cascade laser operating at room temperature. A record high transmission rate up to 6 Gbps over 50-cm link distance is demonstrated at 4.65 mu m wavelength., QC 20220811Part of proceedings: ISBN 978-1-6654-3868-1

Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE., QC 20200603

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is an attractive technology for achieving mid-IR and terahertz (THz) radiation enabled by nonlinear frequency conversion, because of its low two-photon absorption (2PA) down to 1 µm. High crystalline quality of OP-GaP template and subsequent thick layer growth is required to exploit the benefit of low 2PA of GaP pumped with short wavelength lasers [1]. In this work, we present the development of heteroepitaxial growth of OP-GaP on wafer fused OP-GaAs template with high growth rate and good domain fidelity. The conductivity of the GaP grown on planar GaAs was investigated in the THz region., SyskonpostNot duplicate with DiVA 1429993QC 20200623

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is an attractive technology for achieving mid-IR and terahertz (THz) radiation enabled by nonlinear frequency conversion, because of its low two-photon absorption (2PA) down to 1 pm. High crystalline quality of OP-GaP template and subsequent thick layer growth is required to exploit the benefit of low 2PA of GaP pumped with short wavelength lasers [1]. In this work, we present the development of heteroepitaxial growth of OP-GaP on wafer fused OP-GaAs template with high growth rate and good domain fidelity. The conductivity of the GaP grown on planar GaAs was investigated in the THz region., QC 20200513

QC 20220301Conference ISBN: 978-1-7281-0469-0

Heteroepitaxial growth of orientation-patterned GaP on patterned GaAs template was developed by using hydride vapor phase epitaxy for quasi-phase-matching applications. We present the growth with well-defined periodic boundaries between (001) and (00 1) GaP domains. The GaP layer on planar GaAs was characterized by terahertz time-domain spectroscopy and the conductivity of GaP (0.16 S cm-1) was obtained in terahertz range., Not duplicate with DiVA 1366349Part of proceedings: ISBN 978-1-7281-0080-7QC 20230921